Accelerated directed evolution for trait improvement requires increased genetic diversity to produce new, beneficial alleles of yield- and quality-related traits. However, many current methods randomly affect the whole genome (mutagenesis) or drag in potentially deleterious alleles of linked genes (wide crosses). By contrast, in accelerated synthetic directed evolution, CRISPR-based technologies produce localized, targeted sequence diversification; subsequent selection or screening allows us to identify new alleles with the desired phenotype for the target trait. We develop technologies for localized and targeted sequence diversification and selection under selective pressure to evolve beneficial traits.